Method of heating cellulose digesting liquors



March 1, 1932. i A BRQBECK '1,847,589

METHOD OF HEATING CELLULOSE DIGESTING LIQUORS Filed Feb. 14, 1929 mi 7 v Patented Mar. 1, 1932 I 1,847,589

UNITED STATES PATENT oFFlcE I .ARNOLD BROBECK, F BOMHUS, NEAR GEVLE, SWEDEN Application led February 14, 1929,`Seria1 No. 339,944, and in Sweden February 18, 1928.

On directly heating liquors used for digestthe-speed of the liquor relatively to the heating cellulose-containing material said liquors ing surfaces ought to'be about 2.5 meters per have a tendency to form solid incrustations second. If the content of CaO is 1% and on the heating surfaces, which is a very great the steam temperature is l165" C., the speed 5 inconvenience, as they considerably reduce of the liquor ought not to be lower than about l5 the transmission of heat,cause interruptions l1.5 meters per second. in the manufacturing for cleaning purposes A form of an apparatus for executing the etc. It is especially on evaporating acid `liqlpresent invention is illustrated on the accomuors for the sulphite cellulose method acpanying drawing, showin schematically an cording to the indirect circulation method apparatus in vertical sectlon, some parts be- 60 that these inconveniences occur. ing, however, shown in elevation.

The inventor has found, that the reason of 1 designates a receptacle with walls 2 and the formation of said incrustations on the 3.. At one end said receptacle is provided heating surfaces is principally depending on with a cover 4 and tube plate 24, and between the fact, that the liquor has hitherto, princisaid plate and the wall 3 there is formed a 65 pally due to improper construction of the chamber 5, which is provided with an outlet heating apparatus, passed over the heating 26. At the opposite end of the receptacle surfaces with too low a speed, which results there is a wall 6 located at a suitable distance in local superheating of the liquor. from the wall 2, and between said walls there The method forming the object 0f the presis formed a chamber 7, provided with an inlet ent invention is based upon this observation, 18. At a further distance from the wall 6 and the liquor is therefore in a special manthere is another wall 8, and between the walls ner caused to pass along the heating elements 6 and 8 there is formed a chamber 9. This with a relatively high speed, and it has been end of the receptacle is provided with a cover found, that in this manner it has been possible 10, and between the said cover and the wall 8 75 in practice to avoid the formation of incrustathere 1s formed a chamber 11, which is protions 0n the heating surfaces, Vldeq. Wlth' 8.11 inlet 12. The Chamber 9 According to the invention a relatively provlded with an outlet 13. high number of heating ,elements are used Longltufllnally throu hV the receptacle 1 in the apparatus, and theiinvention is charthere are located a num r of tubes 14, ex- 90 acterized by the fact, that the liquor is by tending between the walls 2 and 3, thus conmeans of special guiding members divided ncctlng the chambers 7 and 5 with one aninto a great number of relatively thin streams, Other.

which are caused to move along the heating Wlthln these tubes there are located narelements with a speed, which is, with regard rower tubes 15, which are closed at one end 85 'to the momentary conditions relating t0 the and extend from the wall 6 through the tubes ,temperature of the heating medium and the 14- Their Outer ends are supported -by a composition of the liquor, so high that practitubeplate 24, so that they are securely held cally n0 incrustationg are formed on the 1n a central position with relation to the tubes 40 heating Surfaces, 14. Within the tubes 15 are located nar- 9 As heating medium steam is generally rower tubes 16 attached in the wall 8 and used, although it may also be possiblel to use extending through the tubes 15 to the vicinity other liquid or gaseous heating agents. The of the closed ends of the same. The tubes 16 speed of the liquor along the heating surfaces are open at both ends.

is, as previous y set forth, dependent 0n the From this construction it will be clear, that 95 composition of the liquor and the temperature the tubes v16 communicate with the chamber of the heating medium. As an example it 11. The tubes 15 communicate with the may be set forth, that on evaporating'sulphite Chamber 9, yand the tubes 14 form acommunidigesting liquor with a contentof 1.3% of cation between the chambers 7 and 5.

5 0 CaO and ata steam temperature ofv185 C. Suppose that the apparatus in question is -100 used for indirectly heating sulphite digesting liquor according to the circulation method. The liquor is then introduced from the boiler (not shown) by aid of a pump or the like through the conduit 18 into the chamber 7, from which the same is by means of a pump or the like 'caused to pass with a high speed through the intermediate space between the tubes 14 and 15 (the tubes 14 serving as guides) and into the chamber 5 and from there through the outlet 26 and back to the boiler and from there again into the chamber 7 etc.

The quantity of the liquor introduced into the apparatus is thus divided into a great number of relatively thin ring or tube-shaped streams surrounding the heating elements 15.

Steam is introduced through the conduit 12 into the chamber 11 and passes therefrom through the tubes 16 against the bottoms of the tubes 15 and from there back through the tubes 15 to the chamber 9, from where steam and water of condensation are removed through the conduit 13. The tubes 15 thus form the heating elements, and the liquor passes through the intermediate spaces between the tubes 15 and 14 with a relatively high speed. By this means local superheating of the digesting liquor is avoided and consequently also the formation of incrustations on the heating surfaces.

By applying the present invention it has een found in practice, that it will be possible to avoid in an eicient manner the above mentioned inconveniences on evaporating digesting liquors of the kind set forth.

The steam introduced into the chamber 11 generally has a temperature of more than 110 C., and generally it is convenient to maintain the liquor under a higher pressure when passing through the tubes 14, than it has in the boiler. This result can be obtained by throttling the outlet tube 26 by means of a valve or the like.

It is evident, that the above described apparatus can be modified in several ways without departing from the scope of the invention. So for instance it will be possible to place spiral-shaped guides in the interme- 5 diate spaces between the tubes 14 and 15 so as to cause the liquor to move along a spiralshaped path. Nor is it necessary to have the tubes 14 and 15 located vertically, as they may also have an oblique or horizontal posiis also provided with a number of tubes, serving as heating elements, the liquor has been caused to pass substantially across the heating elements, no guides being in this case provided to cause the liquor to pass in a great number of relatively thin streams along the heating elements. In said apparatus it has therefore been impossible to avoid the formation of incrustations, although the liquid has passed with a relatively high speed through the. apparatus.

Such evaporating methods are also known, according to which the vapours, developed from the liquor, are compressed and again used as heating medium, the liquor being forced through tubes .heated by said compressed vapours. This is, however, a special case, which has nothing to do with heating methods of the kind described, as the said previous method has for its object to obtain a workable method in the special case, when the temperature-difference between the compressed heating vapours and the liquor is only 2 or 3 C., in which case there isno risk for superheating the liquor in contact with the heating surfaces, and, consequently, much less risk for the formation of incrustations.

I' claim:

The method of preventing the formation of incrustations on heating surfaces while conducting sulphite cellulose digestingliquor in contact with said heating surfaces, c011- sisting in dividing the liquor into a great number of relatively thin tube-like streams defined by said heating surfaces, applying heat at a temperature ranging from 110 C. to 185 C. to the inner surfaces of said tubelike stream-s, forcing said liquor streams at all points of travel at a velocity of at least 1.5 meters per second to thereby prevent boiling of the liquor and precipitation of monosulphite on the heating surfaces.

In testimony whereof I have hereunto afxed my signature.

ARNOLD BROBECK. 

